Due to commit f7be53ac9dac85b83e7fe5ecede01b98a572ba48, these errors will no longer show in GHC 7.8. However, I feel that the testsuite is now giving a false sense of security in terms of dynamic linking. Obviously dynamic linking was broken in 7.6, but the testsuite did not catch it!

Sadly, this behaviour can now only be verified in the 7.6 branch, and not in 7.8 or HEAD.
Hopefully somebody more knowledgeable of the testsuite can comment why dynamic linking worked when an executable was run "within" the testsuite, whilst being broken when run normally.

Of course, DYLD_LIBRARY_PATH was never set for executables that ran "outside" of the testsuite.
So in a way, the testsuite and an installed GHC were "misaligned".
Seeing how as of 7.8 the testsuite and an installed GHC are "aligned", I guess the status of this ticket should be turned to either solved or wontfix?

No, it does not mean that we can refrain from setting DYLD_LIBRARY_PATH. in f7be53ac9dac85b83e7fe5ecede01b98a572ba48, the rpaths are made relative to the final install location. During testing, the libraries are still in their build locations, so we still need DYLD_LIBRARY_PATH to find the libraries.